Phenol alkylation process



United States Patent 3,133,974 PHENOL ALKYLATEQN PRGCESS Robert P. Carryand James C. Geddes, in, Baton Rouge, La, assignors to EthylCorporation, New York, N.Y., a corporation of Virginia No Drawing. FiledNov. 23, 1060, Ser. No. 71,163 12 Claims. (Cl. 260-624) This inventionrelates to a novel low temperature process for the simultaneouspreparation of ortho alkyl phenols, 2,4-dialkyl phenols and 2,6-dialkylphenols. More particularly, this invention relates to a novel lowtemperature process for the conjoint production of substantialquantities of ortho-tert-butyl phenol, 2,4-di-tertbutyl phenol and2,6-di-tert-butyl phenol.

Of the various known alkylated phenols, ortho-tertbutyl phenol,2,4-di-tert-butyl phenol and 2,6-di-tert-butyl phenol are particularlyvaluable in the chemical and allied arts. By way of example,2,6-di-tert-butyl phenol is extensively used commercially as anantioxidant and as a necessary ingredient in the preparation of4,4'-methylene bis-2,6-di-tert-butyl phenol, a superlative antioxidantfor lubricating oils and other oxygen-sensitive organic media (US.Patents 2,944,086; 2,807,653). Similarly, 2,4-ditert-butyl phenol is theessential raw material for the production of 2,2'-methylenebis-2,4-di-tert-butyl phenol, another important antioxidant (US. Patents2,807,653; 2,758,032). By the same token, ortho-tert-butyl phenol is anexceedingly valuable chemical intermediate, e.g. for use in theproduction of novel phenol-formaldehyde resins of unique properties.

Current commercial activities have imposed a demand for a process whichcan efiiciently, effectively and conjointly produce these three tertiarybutylated phenols from phenol and isobutylene. However, the provision ofsuch a process is complicated by the facts that the process to fulfillthis demand must not require high temperatures and must not produce anoverabundance of 2,4,6-tri-tertbutyl phenol. Even temperatures as highas l80200 C. in such a process are very undesirable in that dealkylationand rearrangement of the tertiary butyl phenols may be encountered.Furthermore the need to supply heat sufiicient to raise large quantitiesof reactants to such elevated temperatures in a commercial installationsignificantly increases the cost of the process and the consequentproducts. The compound 2,4,6-tri-tert-butyl phenol which is readilyformed when phenol is alkylated with isobutylene is a millstone becausethere is no particular present commercial outlet for this material andit cannot be economically converted back into the above three desired,commercially important tertiary butyl phenols. Therefore, the conversionof phenol into 2,4,6-tri-tertbutyl phenol represents a distinct Waste,both of valuable raw materials and of throughput in a commercialoperation. As a consequence, there is a distinct need in the art for alow temperature process whereby phenol and isooutylene can beselectively converted into significant quantities of ortho-tert-butylphenol, 2,4-di-tert-butyl phenol and 2,6-di-tert-butyl phenol withoutthe formation of excessive quantities of 2,4,6-tr-i-tert-butyl phenol.

Accordingly, an object of this invention is to fulfill the foregoingneed. More particularly, an object of this invention is to provide a lowtemperature process whereby ortho-tert-butyl phenol, 2,4-di-tert-butylphenol and 2,6- di-tert-butyl phenol are concurrently formed insignificant quantities without incurring the formation of aninordinately high amount of 2,4,6-tri-tert-butyl phenol. Other objectswill become apparent from the ensuing description and claims.

The above and other objects have now been accomplished in a veryefiective, efficient and economical manner by the process of thisinvention. We have discovered 3,133,974 Patented May 19, 1964 that bysubjecting a reaction mixture composed of phenol, isobutylene, analuminum phenoxide catalyst and at herematter-defined halogen compoundto a temperature of from about 120 to about 160 C. and a pressure offrom about to about 900 p.s.i.g., an eflicient simultaneous conversionto ortho-tert-butyl phenol, 2,4-di-tert-butyl phenol and2,6-di--tert-butyl phenol is accomplished, while at the same time, thecoproduction of 2,4,6-tri-tert-butyl phenol is efiiectively suppressed.

In this process there should be present from about 2 to about 5 moles ofisobutylene per each mole of phenol used. This ratio is preferred fromthe standpoint of optimum reaction rates. However, higher amounts ofisobutylene can be used (e.g. 6 to 8 moles per mole of phenol) whenusing temperatures approaching 160 C. Conversely, a ratio of as low asabout 1.5 mole of isobutylene per mole of phenol can be used, especiallyat temperatures approaching C.

In carrying out our process, it is essential to have present in thereaction zone one or more halogen compounds, viz. hydrogen halides,saturated organic halides or mixtures thereof. While the precise roleplayed by this halogen compound in the mechanism of the process has notbeen totally established, a vast amount of experimental evidencedefinitely indicates that this material is not a catalyst or a catalystpromoter. Instead, its presence in the reaction zone beneficially altersthe course of the reaction so that the ortho-tert-butyl phenol,2,4-di-tert-butyl phenol and 2,6-di-tert-butyl phenol are conjointlyformed in substantial quantities. This is borne out by the fact that ifthe halogen compound is omitted from the reaction system these threetertiary butylated phenols are not conjointly formed in substantialquantities.

Preferred halogen compounds include tertiary butyl chloride, hydrogenchloride and mixtures thereof although other hydrogen halides andsaturated organic halides (e.g. tertiary butyl bromide, ethyl chloride,hydrogen bromide, propyl iodide, etc.) can be used.

The relative proportions of several of the ingredients of the reactionmixture are very important. Thus the reaction mixture of the process ofthis invention initially contains (a) from about 0.002 to about 0.014gram atom of aluminum as the aluminum phenoxide catalyst per gram moleof phenol, and (b) from about 0.1 to about 3 gram moles of the halogencompound per gram atom of aluminum in the catalyst. Generally speaking,as the aluminum concentration is decreased within the foregoing rangethe amount of the halogen compound should be decreased within theforegoing range, although this feature is not essential to the practiceof this invention. In addition, when the lower concentrations of halogencompound are used it is desirable to use temperatures approaching theupper limit described above.

The great importance of the aluminum phenoxide catalyst concentration isshown by the fact that when a process meeting all of the qualificationsof the process of this invention except that a somewhat higherconcentration of aluminum phenoxide catalyst was used, the reactionmixture never contained any more than 4 mole percent of 2,6-di-tert-butyl phenol. Thus in the process of this invention a relativelysmall amount of aluminum phenoxide catalyst must be used in order toinsure the formation of an adequate amount of 2,6-di-tert-butyl phenoleven though it was known heretofore (US. 2,831,898) that aluminumphenoxides are excellent selective catalysts for use in the preparationof 2,6-di-tert-butyl phenol. It is seen, therefore, that the process ofthis invention is enigmatic.

Another technical anomaly presented by our process is the fact that ifthe amount of halogen compound is too high (i.e. exceeds the amountspecified above), the objects of this invention are not accomplished. Infact, even though larger quantities of aluminum phenoxide catalyst beused, the use of higher concentrations of halogen compound results in amixture which is very poor in 2,6-ditert-butyl phenol content andexcessively rich in 2,4,6-tritert-butyl phenol content.

Practicalities demand that the reaction mixture contain at least 10 molepercent each of ortho-tert-butyl phenol, 2,4-ditert-butyl phenol and2,6-di-tert-butyl phenol so that these three valuable materials can berecovered without too much difficulty and without imposing a severeeconomic penalty upon the process or its valuable products. By the sametoken, an overabundance of 2,4,6-tritert-butyl phenol in the reactionmixture imposes a like economic penalty upon the process since itrepresents waste not only of valuable raw materials but of reactorthroughput. Accordingly, we prefer to operate our process under theabove-described conditions for a time ranging from between that time atwhich ortho-tert-butyl phenol, 2,4-di-tert-butyl phenol and 2,6-di-butylphenol all become present in the reaction mixture at a concentration ofat least about 10 mole percent (based upon the total phenolic compoundspresent in the mixture) to that time at which the mole pecentage ratioof Orrho-tel't-butyl plzenl+2,4-di-tert-butyl phen0l+2,6-di-tert-butylphenol 2,4,6-tri-tert-butyl phenol no longer exceeds about 2.5. However,in situations Where phenol and isobutylene raw materials are readilyavailable at low costs this mole percentage ratio can be extended downto about 2.0 provided, however, that the three desired tertiarybutylated phenols are present in the reaction mixture to absoulte molarconcentrations of at least percent each.

When it is desired to have the content of ortho-tert-butyl phenolpredominate in the reaction product over the contents of the 2,4- and2,6-di-tert-butyl phenols, the amount of aluminum phenoxide catalystshould generally be no higher than about 0.008 gram atom of aluminum pergram mole of phenol initially charged to the reactor. Another way ofachieving this same result is to employ commercially available phenolwithout any special precautions of purification prior to use and toemploy therewith a concentration of aluminum phenoxide catalyst rangingup as high as about 0.014 gram atom of aluminum per gram mole of suchphenol initially used. Without desiring to be bound by any theoreticalconsiderations, it is our belief that trace amounts of moisture presentin most commercially available grades of phenol will deactivate a slightportion of the aluminum phenoxide catalyst so that the ortho-tert-butylphenol content in the reaction product will predominate over thecontents of the 2,4- and 2,6-di-tert-butyl phenols. Conversely, when thecontent of 2,4- and 2,6-di-tert-butyl phenols is intended to predominateover the ortho-tert-butyl phenol content, the amount of catalyst shouldbe in the range of about 0.010 to about 0.014 gram atom of aluminum pergram mole of phenol initially charged to the reactor. This same effectcan be achieved by using even somewhat lower concentrations of thealuminum phenoxide catalyst provided that the phenol used in the processis essentially anhydrous. It will be understood, of course, that theprocess of this invention should be carried out under relativelyanhydrous conditions. Therefore, either the reactants and the reactionsystem should be kept essentially anhydrous or, where this is notpossible or feasible, the reaction system should be kept essentiallyanhydrous and a somewhat larger quantity of aluminum phenoxide catalystshould be formed within or charged into the reaction vessel. By carefulselection of the amount of catalyst so employed, a portion thereof willserve to dry up the reaction system and leave the desired concentrationof aluminum phenoxide catalyst for operation in accordance with thisinvention.

The aluminum phenoxide catalyst used in the process of this inventioncan be prepared in a number of ways.

One method is to react phenol directly with aluminum metal to form thealuminum phenoxide. Another method is to react phenol with an aluminumderivative of an acid which is weaker than phenol. Still another methodof preparing the catalyst is to react a salt of phenol such as sodiumphenoxide with a halide of aluminum such as AlCl AlBr etc. In short, anyknown process by which an aluminum phenoxide can be formed can be usedin the practice of this invention. In general, we prefer to use as thecatalyst a compound which initially is aluminum triphenoxide, althoughduring the course of the reaction the chemical make-up of this phenoxidecatalyst may become altered either by alkylation of one or more of thephenoxide rings by the isobutylene, or by replacement of one or more ofthe phenoxide rings, by a corresponding number of alkylated phenoxidegroups from the alkylated phenols formed in the reaction system. Hence,if desired, the initial aluminum phenoxide catalyst may be formed fromortho-tert-butyl phenol or the like. However, when this method isemployed, the alkyl substituents on the phenol should be one or moretertiary butyl groups so that the high purity of the reaction product isnot impaired by the liberation of other phenolic ingredients during theprocess.

The catalyst can be preformed or prepared in situ. However, there arecertain advantages in utilizing as in situ formed catalyst. One suchadvantage is that a separate reaction step becomes unnecessary and theamount of materials to form the requisite concentration of catalystso-formed can be readily calculated beforehand. Furthermore, methods areknown by which one or more of the above-described halogen compounds canbe formed as a by-product during the course of the aluminum phenoxidecatalyst preparation. For example, aluminum chloride can be prereactedin situ to form aluminum triphenoxide and the requisite concentration ofhydrogen chloride.

This invention will be still further understood by reference to thefollowing examples in which all parts and percentages are by weightunless otherwise specified.

EXAMPLE I An alkylation run of this invention was conducted in abatchwise manner, employing a heated reaction vessel equipped with astirring means and a means for introducing and withdrawing chemicalreagents. During the course of the run, the vessel was heated andagitated, and samples of the reaction mixture were taken at frequentintervals and analyzed by gas chromatography to determine the nature andquantity of each component therein. In this run, the aluminumtriphenoxide catalyst was present at a concentration of 0.01 gram atomof aluminum per gram mole of phenol and tertiary butyl chloride waspresent throughout the reaction. The concentration of chlorinecorresponded to 3 gram atoms thereof per each gram mole of the aluminumcatalyst. This isobutylene concentration was equivalent to approximately4 moles thereof per each mole of phenol. During the course of thereaction, the temperature was maintained at approximately 150 C. and thepressure ranged from approximately 400 to 130 p.s.i.g. The make-up ofthe reaction mixture after operation for minutes under the aboveconditions is shown in Table I.

Table I PROCESS OF THIS INVENHFIONPRODUCT DISTRIBU- TION AFTER 90MINUTES OF OPERATION Product distribution,

Phenolic component: mole percentages 2,4-di-tert-butyl phenol 102,6-di-tert-butyl phenol 13 Ortho-tert-butyl phenol 492,4,6-tri-tert-butyl phenol 4 Phenol 20 Para-tert-butyl phenol 4 It willbe seen that at about 90 minutes each of the ortho- Phenolic component:mole percentages 2,4-di-tert-butyl phenol 14 2,6-di-tert-butyl phenol 19Ortho-tert-butyl phenol 50 2,4,6-tri-tert-butyl phenol 8 Phenol 6Para-tert-butyl phenol 3 From the above data it is seen that the molepercentage ratio of ortho-tert-butyl phenol-j-ZA-di-tert-butylphenol+2,6di-tert-butyl to 2,4,6-tri-tert-butyl phenol was about 10.

EXAMPLE II Another alkylation runof this invention was conducted asdescribed in Example I with the exception that the pressure ranged fromapproximately 375 to 238 p.s.i.g. The make-up of the reaction mixtureafter operation for varying times ranging from minutes to 70 minutesunder the above conditions is shown in Table III.

Table III PROCESS OF THIS INVENTION-PRODUCT DISTRIBU TION AFTER VARIOUSPERIODS OF OPERATION (25-70 MINUTES) Product distribution, molepercentages Phenolic component Minutes 2,4-Di-tert-buty1 phenol 25 24 2221 19 18 15 14 2-6-Di-tert-butyl phenol 10 13 15 18 22 25 32 36Ortho-tert-butyl phenol 33 33 33 32 30 28 21 16 2,4,6-Tri-tert-butylphenol 19 21 23 25 27 28 32 33 9 7 6 4 3 3 2 1 Para-tert-butyl phenol 43 2 1 1 l nil nil The data shown in Table III establish that throughoutthe indicated time period, the individual mole percentages ofortho-tert-butyl phenol, 2,4-di-tert-butyl phenol, and 2,6-di-tert-butyl phenol each exceeded 10 mole percent. In this run, thetime period ranging from about 25 to about 50 minutes of operationconstitutes a preferred embodiment of this invention since in all casesthe molar percentage ratio of ortho-tert-butyl pheno1+2,4-di-tert-butylphenol+2,6-di-tert-butyl phenol to 2,4,6-tri-tert-butyl phenol was atleast 2.5. The time period of from about 50 to about 70 minutes,however, comes within the purview of this invention inasmuch as theforegoing ratio during this period wasat least 2.

COMPARATIVE EXAMPLE An alkylation run not of this invention wasconducted in approximately the same manner as described in Example Iexcept for the fact that the aluminum triphenoxide catalystconcentration was somewhat higher than that used in our process. In allother respects, this run was in accordance with the procedure providedby our invention. In particular, the run was carried out in a batch-wisemanner,

employing a heated reaction vessel equipped with a stirring means andmeans for introducing and withdrawing chemical reagents. During thecourse of the run the vessel was heated and agitated, and samples of thereaction mixture were taken at frequent intervals over the period of 168minutes of operation to determine the nature and quantity of eachcomponent therein. In this run the aluminum triphenoxide catalyst waspresent at a concentration of 0.017 gram atom of aluminum per gram moleof phenol and tertiary butyl chloride was present throughout thereaction. The concentration of chlorine corresponded to 3 gram atomsthereof per each gram mole of aluminum catalyst. The isobutyleneconcentration was equivalent to approximately 4 moles thereof per eachmole of phenol. The temperature was maintained at approximately 150 C.throughout the reaction and during this time the pressure ranged fromapproximately 320 to 210 p.s.i.g. It was found that at no time duringthe course of the reaction did the concentration of 2,6-di-tert-butylphenol exceed 4 mole percent based on the total phenolic content of thereaction mixture. Consequently, this run completely failed to achievethe objects of this invention.

As indicated by Examples I-II, the process of this invention can beconducted in a batchwise manner by adding all of the necessaryingredients to the reaction vessel, sealing the same, and heating thesystem to the requisite temperature for the appropriate period of time.It is desirable to provide for sufficient agitation of the reactionsystem during the process to insure thorough mixing of the variouscomponents of the system. Alternatively, the isobutylene may be fed intothe reaction system in incremental portions or continuously (asemi-batch procedure) during the run.

Tertiary butylation of phenol in accordance with this invention can beconducted in a continuous manner by passing the reactants, the aluminumphenoxide catalyst and the halide compound in appropriate proportionsthrough a reaction zone where they are subjected to the conditions ofheat, pressure, and mixing necessary to accomplish the objects of thisinvention. ln such an embodiment, any unreacted phenol or isobutylene,or both, can be recycled into the reactor.

When the reaction has reached the appropriate product distribution(either in a batch or in a continuous operation) the reaction mixtureshould be contacted with a suffioient quantity of water, aqueous causticsolution or aqueous acid solution to hydrolyze the catalyst and stop thereaction. To do this, the reaction mixture is usually cooled and chargedto a vessel containing the water, aqueous caustic solution, or aqueousacid (e.g. HCl solution). The ortho tert-butyl phenol,2,4-di-ter-t-butyl phenol and 2,6-di-tcrt-butyl phenol are recoveredfrom the resultant reaction mixture by distillation, extraction or likepro cedures. To efiect this separation, the use of fractionaldistillation especially at reduced pressure is particularly desirable.

In efiecting the process of this invention, it is preferred to use fromabout 0.005 to about 0.012 gram atom of aluminum as the aluminumphenoxide catalyst (most preferably as aluminum triphenoxide) per grammole of phenol and from about 1 to about 3 gram atoms of the halogen(most preferably chlorine) as the halogen compound per gram mole ofaluminum catalyst. In this manner, the maximum benefits characterizingthis invention are achieved especially at temperatures ranging fromabout to about 160 C. and pressures ranging from about to about 500p.s.i.g.

The use of an inert diluent is unnecessary in effecting our processalthough it is within the purview of our invention to use such areaction diluent. Paraffins, cycloparaflins, and aromatic hydrocarbonsare examples of suitable inert diluents which are compartible with thecomponents of our reaction system and which, therefore, can be used fordiluent purposes. If desired, an inert gas such 7 as nitrogen, argon,helium, krypton or gaseous parafi'lnic hydrocarbons can be used as aninert atmosphere.

While this invention has been described with particular reference to thealkylation of phenol with isobutylene, it will be understood that theprinciples of operation herein described can be applied verysuccessfully to the alkylation of other phenols such as meta-cresol,ortho-tert-butyl phenol, ortho-isopropyl phenol, and the like.Furthermore, it is within the ambit of this invention to apply our novelprinciples of operation to the alkylation of phenol or other phenoliccompounds (such as those just described) using propylene or the variouspentenes, hexenes, heptenes, octenes, etc. which are normally applicablefor use as reactants in phenol alkylation procedures. Generallyspeaking, the reaction conditions described herein are directlytranslatable to effecting such other processes. -Any slightmodifications which may be desirable will, of course, now be apparent toone skilled in the art.

We claim:

1. A process for the conjoint preparation of ortho'tertbutyl phenol,2,4-di-tert-butyl phenol and 2,6-di-tert-butyl phenol characterized bysubjecting a reaction mixture composed of phenol,

isobutylene, an aluminum phenoxide catalyst and a halogen compound, ashereinafter defined, to a temperature of from about 120 to about 160 C.,and

to a pressure of from about 100 to about 900 p.s.i.g. tor a period oftime ranging from that (a) time at which each of ortho-tert-butylphenol, 2,4-di-tert-butyl phenol, and 2,6-di-tert-butyl phenol becomespresent in the reaction mixture a concentration of at least about 10mole percent based on the total phenolic compounds present in saidmixture, to that (b) time at which the mole percentage ratio ofortho-tert-butyl phenol-{-2,4-di-te-rt-butyl phenol+2,6-di-tert-butylphenol 2,4,6-tri-tert-butyl phenol 8 of aluminum as said catalyst pergram mole of phenol and (b) from about 0.1 to about 3 gram moles of saidhalogen compound per gram atom of aluminum as said catalyst.

2. The process of claim 1 wherein said catalyst initially ispredominantly aluminum triphenoxide.

3. The process of claim 1 wherein said halogen compound consistsessentially of tertiary butyl chloride.

4. The process of claim 1 wherein said halogen compound consistsessentially of hydrogen chloride.

5. The process of claim 1 wherein said catalyst initially ispredominantly aluminum triphenoxide and said halogen compound consistsessentially of tertiary butyl chloride.

6. The process of claim 1, wherein said catalyst initially ispredominantly aluminum triphenoxide and said halogen compound consistsessentially of hydrogen chloride.

7. The process of claim 1 wherein said aluminum phenoxide catalyst isformed in si-tu.

8. The process of claim 1 wherein the isobutylene is used in an amountof from about 2 to about 5 moles per each mole of phenol.

9. The process of claim 1 wherein the temperature is in the range ofabout to about 160 C. and the pressure is in the range of about to about500 p.s.i.g.

10. The process of claim 1 wherein the mole percentage ratio ofortho-tert-butyl phenol+2,4-di-tert-butyl phenol+2,6-di-tert-butylphenol 2,4,6-tri-tert-butyl phenol References Cited in the file of thispatent UNITED STATES PATENTS 2,931,898 Ecke et al Apr. 22, 1958 FOREIGNPATENTS 1,044,825 Germany Nov. 27, 1958

1. A PROCESS FOR THE CONJOINT PREPARATION OF ORTHO-TERTBUTYL PHENOL,2,4-DI-TERT-BUTYL PHENOL AND 2,6-DI-TERT-BUTYL PHENOL CHARACTERIZED BYSUBJECTING A REACTION MIXTURE COMPOSED OF PHENOL, ISBUTYLENE, ANALUMINUM PHENOXIDE CATALYST AND A HALOGEN COMPOUND, AS HEREINAFTERDEFINED, TO A TEMPERATURE OF FROM ABOUT 120 TO ABOUT 160*C., AND TO APRESSURE OF FROM ABOUT 100 TO ABOUT 900 P.S.I.G. FOR A PERIOD OF TIMERANGING FROM THAT (A) TIME AT WHICH EACH OF ORTHO-TERT-BUTYL PHENOL,2,4-DITERT-BUTYL PHENOL, AND 2,6-DITERT-BUTYL PHENOL BECOMES PRESENT INTHE REACTION MIXTURE A CONCENTRATION OF AT LEAST ABOUT 10 MOLE PERCENTBASED ON THE TOTAL PHENOLIC COMPOUNDS PRESENT IN SAID MIXTURE, TO THAT(B) TIME AT WHICH THE MOLE PERCENTAGE RATIO OF